Surgical staples and ligating clips are beginning to come into wide use in the surgical profession as an alternative to sutures and ligatures. One advantage of clips and staples in comparison with sutures and ligatures is that tissue fastening or ligating with a staple or clip, whether applied singly or as an array applied in a row or in a ring, is much simpler and faster than with a suture or a ligature. Surgical procedures can be speeded up, thereby reducing the length of time the patient must be anesthetized and shortening the operating room time. Thus, there are both medical and economic reasons for the shift to staples and clips from sutures and ligatures.
The first surgical staples to be used, and still the majority being used, were metal staples. But metal staples, when used externally, must be removed, with accompanying patient discomfort. And when metal staples are used internally, they are left in place. While the metal staples are tiny and become encapsulated by natural processes, and little or no difficulty has been associated with such staples left in the patient, for internal applications surgeons would prefer to use absorbable materials that eventually disappear after their usefulness has ended. For this reason, there is a substantial incentive to develop an absorbable plastic surgical staple.
It appears to be out of the question to produce an absorbable plastic surgical staple of reasonable size that fastens simply by bending back on itself in a manner analogous to the way metal staples fasten. The available absorbable plastics simply lack the required combination of ductility and stiffness that would be required for this purpose. For this reason, the initial attempts to produce an acceptable absorbable plastic surgical staple has concentrated on the fastener/receiver type of staple. In this type of staple, a fastener member includes a base and one or more attached legs which are designed to pierce the tissue to be fastened and to enter receptacles in the receiver on the other side of the tissue. The receiver holds the legs tightly, with the tissue being held between the fastener member and the receiving member. The desirable characteristics of such a staple are the following:
(1) adequate stiffness in the legs to pierce the tissue without being deflected in such a way that they fail to meet the receptacles in the receiver;
(2) adequate strength in the receiver to hold the legs;
(3) strength retention in situ for a period which may vary from about three to six weeks, depending on the function of the staple;
(4) dimensional stability at moderately elevated temperatures, e.g., up to 85.degree. C.;
(5) sterilizability; and
(6) ability to be totally absorbed within a reasonable period of time.
It has not proven to be an easy matter to obtain the requisite combination of properties. For instance, early designs of absorbable surgical staples utilized temporary metal reinforcement for the fastener legs during insertion of the staple to insure adequate stiffness. For instance, see Noiles, U.S. Pat. No. 4,060,089 and Green, U.S. Pat. No. 4,402,445. A presently commercial absorbable clip and an early commercial absorbable staple are made from an 80/20 lactide/ glycolide (mol/mol) copolymer. These fasteners have the disadvantage that they are dimensionally unstable when heated to temperatures over 120.degree. F. (49.degree. C.). Therefore, care must be taken in handling these fasteners, because temperatures well over 120.degree. F. are commonly encountered in shipping and storage in the United States during the warmer months.
A later commercial surgical staple is made from a mixture of a lactide/glycolide copolymer (85/15 molar ratio) plus another polymer that is either a homopolymer of glycolide or a 50/50 glycolide/lactide copolymer.
Absorbable ligating clips made from poly(p-dioxanone) have recently been introduced commercially. Metallic ligating clips have been used for some time.
This invention provides an absorbable surgical fastener, such as a surgical staple, a ligating clip, an anastomotic coupler, a fascia closure, or the like, that has an excellent combination of properties.